BIOGRAPHY OF AKUMA NO RIDDLE

At a private girls' boarding school, Myōjō Academy, thirteen girls are transferred into the academy's "10th Year Class Black". Of these thirteen students, twelve are assassins from various backgrounds who are all tasked with assassinating the remaining student, a girl named Haru Ichinose. One of the assassins, Tokaku Azuma, develops feelings for Haru and defects to her side, resolving to protect her from the other assassins.